arm64: docs: Mandate that the I-cache doesn't hold stale kernel text

arm64: docs: Mandate that the I-cache doesn't hold stale kernel text

Although we require that the loaded kernel Image has been cleaned to the
PoC, we neglect to spell out the state of the I-cache. Although this
should be reasonably obvious, it doesn't hurt to be explicit.

Require that the I-cache doesn't hold any stale entries for the kernel
Image at boot.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200423093658.10602-1-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>